tar cf command - copy the differences only

[subhap]

I want to find out if you can use tar cf - to copy only the differences.

Let me explain a little bit. I am copying a few folders from one disk to another disk mount. The initial tar cf - * would copy everything over.

Let's say after a few days the content of on the original disk has changed and I want to only tar (copy) the differences.

How do I do this?

[subhap]

To copy differences or only the files since the last tar date here is the command.

Let's say we did a tar on Feb 9th, 2009 as follows:
(cd /mydata; tar cf - *) | tar xvf -

Today is Feb 11th and we only want to copy the files that have changed since Feb 9th, 2009. The command would be
(cd /mydata; tar cf - --newer 20090209 * ) | tar xvf -